API Schemas

Secure endpoints by validating requests/responses. Use .parse() for strict server-side checks (fast, throws on bad data).

Step-by-Step Example (Express.js)

1. Schema Setup: Define request body shape.
2. Middleware: Wrap .parse() in try-catch for 400 responses.
3. Response: Optionally validate outgoing data.

Full Code

import express from 'express';
import { v } from 'typyn';

const app = express();
app.use(express.json());

const createUserSchema = v.object({
  name: v.string().min(2),
  email: v.string().email().lowercase(),
  age: v.number().min(18).int()
});

app.post('/users', (req, res) => {
  try {
    const user = createUserSchema.parse(req.body); // Throws if invalid
    // Save to DB (pseudo)
    const savedUser = { id: 1, ...user };
    res.json(savedUser);
  } catch (error) {
    res.status(400).json({ error: error.message }); // e.g., "email: Invalid format"
  }
});

// Usage: POST { "name": "Bob", "email": "bob@example.com", "age": 25 }

Expected Output

• Valid Request: { id: 1, name: 'Bob', email: 'bob@example.com', age: 25 } (200 OK).
• Invalid Request (age: "seventeen"): { error: 'age: Expected number' } (400 Bad Request).

DX Tips

• Middleware Helper: Create validate(schema): (req, res, next) => { try { req.body = schema.parse(req.body); next(); } catch (e) { res.status(400).json(e); } }.
• Response Validation: res.json(schema.parse(responseData)) for outgoing safety.
• Try It: Run with ts-node + pnpm add express typyn. Use Postman to test payloads.

Pitfall: Sanitize inputs: Chain .trim() on strings for security.

Back to Guides | Next: Error Handling

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Last updated: October 23, 2025.